Improving marbling through genetics and feed supplements



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Texas Tech University


Growth and quality are two major concerns to producers of meat animals. Lean growth in meat animal will affect the yield of that animal, and the amount of intramuscular fat will affect the quality of that animal. This thesis contains two studies that involved two different methods of producing an animal with improved growth and meat quality. The first study used animal breeding and genetics to produce a swine line with improved growth, marbling and meat quality. The second study used a feed supplement (Ascophyllum nodosum) to manipulate the processes involved in intramuscular fat deposition to produce greater fat deposition without affecting overall animal performance.
Study 1 used two genetic swine lines, a low serum cholesterol (LC) swine line and a modern (M) swine line, that were crossed (LC×LC, LC×M, M×LC, and M×M) to produce a new line with improved weight gain, marbling and overall meat quality. Once weaned animals were penned by cross with three animals per pen. Pigs were weighed every 7 d from birth to end of nursery phase, then every 14 d until harvest at 154 d. Comparison of linear regressions of the LC×M line to the M×M line, and the LC×LC line to the M×LC line found that the LC×M line grew faster (P < 0.05) than the M×M line, and the LC×LC line grew slower (P < 0.05) than the M×LC line. Comparison of linear regressions of the M×M and M×LC lines found that the two lines were not different (P > 0.05) and grew at the same rate. No differences (P > 0.05) were seen in marbling between treatment groups, but LC×LC group tended to have less (P = 0.079) initial juiciness than the M×LC group, and less (P = 0.075) sustained juiciness than both the M×LC and LC×M groups. Offspring from an M line dam had heavier weights at d 14 and from 28-56 d than offspring from LC sows (P < 0.05). Interaction of sire and dam was seen from 0-7 d and from 70-154 d (P < 0.05). From this study two lines were formed with improved growth, but neither had improved marbling and meat quality. Study 2 used English cross steers (n = 32) and heifers (n = 32) that were fed a commercial corn based diet and differentially supplemented with 2% Ascophyllum nodosum to maximized intramuscular fat deposition as determined by quality grade. Cattle were blocked by sex and divided into one control and three treatment groups receiving Ascophyllum nodosum. Treatment 1 (trt 1) received Ascophyllum nodosum from d 36-50 of the feeding period, trt 2 received Ascophyllum nodosum for the last 14 d of the feeding period, and trt 3 which received Ascophyllum nodosum for both d 36-50 and the last 14 d of the feeding period. Cattle were weighted and ultrasounded at the commencement of trial and every 28 d following until they reach an average body weight of 544 kg. No effect for Ascophyllum nodosum supplementation was found on measured performance characteristics. All treatments groups supplemented with Ascophyllum nodosum had higher actual marbling scores (P < 0.05) than controls. Trt 1 was found to have a highest marbling score of 572.5 (P < 0.05) with the control group having the lowest marbling score of 473.75. Trt 1 had a higher (P < 0.05) quality grade than the control group (P < 0.05) and Trt 2 and Trt 3 were not different (P > 0.05) from any other treatment group. Control group had 25% Choice, 62.5% Select; trt 1 had 75% Choice, 18.8% Select; trt 2 had 62.5% Choice, 25% Select and trt 3 had 56.3% Choice and 31.2% Select. Overall, treatment groups had a 39.58 % increase in Choice quality grade and a 37.5 % decrease in Select quality grade when compared to the control group. These two studies revealed that it is difficult to positively affect both lean growth and intramuscular fat. However, through the use of genetic selection and feed supplementation, improvements in lean growth and intramuscular fat deposition can be achieved. Study 1 found that the effect of the dam on growth is often underestimated and more care should be taken when making breeding decisions. Currently many producers are using terminal cross sires to increase the growth of their offspring and the dam lines are bred to have large litters and good mothering ability. Data collected from this trial suggests that the dam also plays an important role in growth, even after lactation. Study two found that the use of Ascophyllum nodosum increases marbling score in English cross cattle without effecting performance. Supplementation from d 36-50 showed the greatest improvement in marbling score. While the mechanism of action for Ascophyllum nodosum as it relates intramuscular fat deposition is unknown the use of Ascophyllum nodosum as a feed supplement can help to improve marbling score in English cross cattle.